1. Technical Field
This invention relates generally to housings for rechargeable batteries, and more particularly to very thin housings utilizing insert molding to reduce the wall thickness.
2. Background Art
Portable, battery-operated, electronic devices seem to be everywhere. From handheld games, to compact disc players, to radios, to personal data assistants (PDAs), to phones, to pagers, it is becoming rare to encounter a person who does not carry at least one portable electronic device with them all the time. People carry the devices for entertainment, for organizational purposes, and for staying connected with others. A common characteristic shared by each of these devices is that they all rely on batteries for portability.
The general trend with such electronic devices is that manufacturers are making them smaller and smaller. Consequently, the batteries must be smaller as well. While some may think that a rechargeable battery is simply an electrochemical cell, commercial rechargeable batteries are actually sophisticated devices that include advanced electronic circuits. For example, a typical rechargeable battery will include a rechargeable cell, electrical contacts, a circuit board, a safety circuit, an optional charging circuit, and occasionally a fuel gauging circuit. All of these components are placed into a housing. As electronic devices get smaller, manufacturers are demanding that the batteries get smaller too.
The most common way to manufacture housings for rechargeable battery packs is injection molding. In the injection molding process, molten plastic is injected into the cavity of a metal mold. The plastic flows throughout the cavity, thereby filling it. When the plastic cools, the mold is opened and the plastic part is removed.
One problem with injection molding is that there is a fundamental limit to the minimum thickness per unit area of walls of any part. This is due to the flow of the molten plastic. If the cavity in the mold includes passages that are too thin, the plastic will not flow properly through these thin regions. Improper plastic flow leads to parts with walls that break easily or have holes in them. The net result is a battery housing with walls that fall apart too easily. The fundamental limit of battery housing wall thickness means that electronic device manufacturers"" designs are limited by battery size. It would be desirable to make a thinner battery pack, thereby allowing electronic device manufacturers to further reduce the size of their devices.
There is thus a need for a battery housing having thinner walls.